(1) Field of the Invention
The invention relates to boundary layer control systems and more particularly to active turbulent boundary layer control using magnetohydrodynamic technology.
(2) Description of Prior Art
It is well known in the art that control of turbulence and vorticity in the boundary layer flow around a marine hull reduces both drag and radiated noise. Additionally, loaded surfaces, such as diving planes and rudders, or thrusting surfaces such as propellers or screws, can operate at higher performance coefficients when boundary layer control systems are used. Various types of active boundary layer control systems have been designed using: heating the hull skin; injecting the micro bubbles; high strain-rate polymers; suction for drawing off inner boundary layer flow; or injection of high velocity flow along the inner boundary layer. The first three types are based on modifying the fluid properties of flow in the turbulent boundary layer. The fourth type of boundary layer control, commonly referred to as suction boundary layer control, depends on drawing off the low speed flow in the boundary layer near the body of a vehicle so that the natural turbulence prediction cycle will be disrupted. The last type is blowing boundary layer control in which an energized stream is injected into the boundary layer, accelerating the inner flow lines thereby reducing vorticity and turbulence.
Each of these systems has had limited success. The weight, volume and power penalties of active boundary layer control systems have made them impractical in many applications. Additionally, energy supply, storage of polymer, injection gas and ducting for active systems creates maintenance and reliability problems and, in the case of combat damage, additional vulnerabilities.